linux-kernel - Re: [PATCH] Revert "serial: 8250: Fix reporting real baudrate value in c

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Message-ID: <20211007144030.naxrzbjkrq7nmhjo@pali>
Date:   Thu, 7 Oct 2021 16:40:30 +0200
From:   Pali Rohár <pali@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Johan Hovold <johan@...nel.org>, Jiri Slaby <jirislaby@...nel.org>,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Revert "serial: 8250: Fix reporting real baudrate value
 in c_ospeed field"

On Thursday 07 October 2021 16:21:30 Greg Kroah-Hartman wrote:
> On Thu, Oct 07, 2021 at 03:31:46PM +0200, Johan Hovold wrote:
> > This reverts commit 32262e2e429cdb31f9e957e997d53458762931b7.
> > 
> > The commit in question claims to determine the inverse of
> > serial8250_get_divisor() but failed to notice that some drivers override
> > the default implementation using a get_divisor() callback.
> > 
> > This means that the computed line-speed values can be completely wrong
> > and results in regular TCSETS requests failing (the incorrect values
> > would also be passed to any overridden set_divisor() callback).
> > 
> > Similarly, it also failed to honour the old (deprecated) ASYNC_SPD_FLAGS
> > and would break applications relying on those when re-encoding the
> > actual line speed.
> > 
> > There are also at least two quirks, UART_BUG_QUOT and an OMAP1510
> > workaround, which were happily ignored and that are now broken.
> > 
> > Finally, even if the offending commit were to be implemented correctly,
> > this is a new feature and not something which should be backported to
> > stable.
> > 
> > Cc: Pali Rohár <pali@...nel.org>
> > Signed-off-by: Johan Hovold <johan@...nel.org>
> > ---
> >  drivers/tty/serial/8250/8250_port.c | 17 -----------------
> >  1 file changed, 17 deletions(-)
> 
> Argh, sorry I missed this, good catch.  I'll go queue this up now,
> thanks.
> 
> greg k-h

I was waiting for a reply in discussion for this patch...
https://lore.kernel.org/linux-serial/20210927093704.19768-1-pali@kernel.org/t/#u

There was no reply, so I was surprised it was taken without any
reaction. I was really in impression that patch is waiting.

So sorry for that.

Johan, could you write comments below original patch, so discussion is
not on two places? I would really like to fix this issue because
c_ospeed contains incorrect value.